Prodrugs that are triggered by cancer biomarkers are attractive because of their potential to be activated preferentially in cancer cells thereby reducing the serious adverse effects associated with conventional chemotherapy. While numerous cancer biomarkers have been discovered, prodrugs triggered by enzymes have been the main focus because enzymes can activate prodrugs via covalent transformations. Thus, a barrier exists in using non-enzyme biomarkers for prodrug-activation because of our poor understanding of how to develop molecules that selectively recognize, and are activated by, biomarkers that cannot facilitate covalent transformations. The existence of this knowledge gap hinders the full scope of prodrugs that can be developed. Thus the long-term vision of this project is to generate non-covalently triggered prodrugs. The objective of this basic-science application, which is a seminal step in achieving our long term goal, is to establish fundamental supramolecular mechanisms for the non-covalent activation of protein inhibitors by microRNA-21 (miR-21), a highly deregulated, oncogenic, miR. The central hypothesis of this application, which we will test via two complementary design strategies (Aim 1 and 2, respectively), is that miR-21 inducible protein antagonists can be achieved by developing DNA-small molecule chimeras (DCs), that undergo a structural switch from a de-activated conformation to an activated state upon binding sequence specifically to miR-21. The specific aims for this project are to develop, (Aim 1) hairpin-forming DCs de-activated by host/guest interactions and (Aim 2) bidentate DCs de-activated via duplex formation with a guide strand, as miR-21 responsive inhibitors of clinically relevant carbonic anhydrase-II (CA-II). In both aims, we will synthesize and characterize the respective DC systems and will probe their ability to undergo miR-21 induced structure-switching to an activated state via a number of spectroscopic experiments (including UV-vis and fluorescence quenching). Subsequently, the differential ability of the de-activated and active DC conformations to inhibit CA-II will be evaluated (via a colorimetric esterase assay). After optimization of the structure of the DC systems (including enhancing CA-II binding and nuclease resistance), we will transfect DCs into cell-lines over expressing (and control cell-lines under expressing) miR-21 and probe CA-II inhibition-derived cell growth arrest. This proposal is innovative because it develops the first examples of activating protein inhibitors in response to miRs. Further, this project will provide impetus to shift general research into examining non- covalent mechanisms for prodrug activation. This work is significant because (a) it is a seminal step in a continuum of research aimed, in the long-term, at developing miR-21 triggered prodrugs, and (b) it will exert a sustained influence on the field of supramolecular chemistry by enhancing our understanding of how key principles of molecular recognition (such as host/guest interactions and multivalency) in combination with DNA assembly and structure-switching phenomena can be used to develop dynamic protein-binders. )